This invention relates to improvements in ventilator valves of the type illustrated in German Publication DT-PS 23 22 913. While prior art valves of this nature will generally serve their basic purpose, they are not fully satisfactory in all respects. Their design does not necessarily insure an optimally tight closure of their flow passage when the same is necessary, as when the excessive temperature of their environment so demands. Nor are such prior art valves designed to automatically function to achieve a valve closed condition irrespective of their installation position. These and other problems evidenced in use of the prior art valves are solved by the present invention.